Personal computing devices equipped with touch sensitive displays are well known and widely used. Such displays allow a user to control a device by “touch inputs”, i.e. by touching a touch sensitive panel typically positioned over a display screen.
Recent advances in so-called “multi-touch” technology have allowed the development of multi-touch devices, whereby a touch sensitive display of device can derive control information from multiple simultaneous touches by a user. Multi-touch technology increases the amount of control a user has over a device and increases the usefulness and desirability of the device.
Development of multi-touch technology has been mainly limited to comparatively small-scale personal computing devices such as smart-phones and tablet computers. However, there is recognition that providing multi-touch touch sensitive displays in other areas could lead to improved devices of other types.
Conventional multi-touch display devices use a so-called “mutual capacitance” technique whereby the level of charge transferred from a first set of conductors (i.e. electrodes) to a second set of conductors by virtue of capacitive coupling is monitored. A reduction in this charge transfer indicates a user touch. Other techniques can be used to detect user touch, such as so-called “self-capacitance” techniques whereby a change in capacitance of isolated conductors arranged in a grid pattern is monitored. However, self-capacitance based techniques perform poorly when trying to distinguish between multiple simultaneous touches and are therefore not appropriate for multi-touch applications.
A conventional mutual-capacitance based multi-touch display device comprises a touch-sensitive panel overlaid on a display screen. The touch sensitive panel includes a first (input) array layer comprising a first set of conducting electrodes and a second (output) array layer comprising a second set of conducting electrodes. The first and second array layers are separated by a number of insulating layers and positioned under a transparent protective substrate usually made from glass. The first and second set electrodes are made from indium tin oxide (ITO). ITO when deposited in thin enough layers becomes transparent and is generally considered to be the best material for use in the panels that are positioned over display screens.
The electrodes of the first array layer are arranged to cross the electrodes of the second array layer at a number of crossing points. Transfer of charge due to capacitive coupling between the electrodes of the first and second layers at the various crossing points is monitored. A user touch (e.g. a user bringing a finger or a capacitive stylus into close proximity or physical contact with the touch sensitive panel) is detected when a drop in the level of charge transferred by capacitive coupling is detected at a crossing point. This is due to charge that would otherwise have been transferred from one electrode layer to the other at the crossing point instead being transferred into the user (or stylus).
There are a number of drawbacks to conventional techniques for providing touch sensitive panels for multi-touch devices. In particular, the processing of information from the output electrode array may be very intensive, reducing responsiveness and deteriorating the user experience. An example of this is the perceived requirement to repeat every sensing scan at every crossing point in order to minimise the effect of noise.
It would be desirable to reduce the processing overhead for touch sensitive displays.
In a first aspect of the invention there is provided a touch sensitive display comprising a sensor having an input array of electrodes and, capacitively coupled thereto, an output array of electrodes; wherein said touch sensitive display comprises a controller operable to perform a scan operation at every intersection point of said input array, said scan operation comprising:    measuring a touch value for an intersection point;    determining the proportional difference between said touch value and a base touch value for said intersection point as a proportion of said base touch value, wherein said base touch value is indicative of there being no touch event on the sensor; and    comparing said proportional difference to a predetermined proportional touch threshold so as to determine whether there is a touch event at that point.
Said controller may be further operable to measure said base touch value for each intersection point.
Said proportional touch threshold may be defined as a the difference between a touch value and a base touch value, as a proportion of said base touch value, indicative of there being a touch event.
Said predetermined proportional touch threshold may be set at any value between 5% and 50%, or at a value between 10% and 30%.
Said sensor may be operable such that a change in voltage applied to one of the electrodes of said input array results in a voltage pulse on the output array electrodes, the magnitude of which is indicative of a touch event.
Each of the electrodes of said input array of electrodes and said output array of electrodes may comprise a conducting wire individually insulated with an insulating coating. The conducting wire may comprise a metallic electrode material such as copper, nickel, tungsten or similar. The conducting wire may be of diameter 8 μm to 18 μm. The insulating coating may comprise a polyurethane coating. The insulating coating may have a thickness of 1 μm to 2 μm.
In some embodiments, the electrodes of said input array of electrodes are arranged substantially orthogonal to the electrodes of said output array of electrodes, each intersection point being where an input electrode crosses an output electrode.
Said input array of electrodes and said output array of electrodes may be laid over each other so as to form a single electrode array layer in the panel. In accordance with these embodiments the electrodes can be laid down on a supporting substrate as a single layer and in a single manufacturing step.
Said controller may be arranged to detect a touch at an intersection point by transmitting a pulse on an input electrode and monitoring a corresponding pulse energy on one or more output electrodes, said corresponding pulse arising due to capacitive coupling between the input electrode and the one or more output electrodes. The touch may be detected at the intersection point upon the controller unit detecting a reduction in pulse energy on one of the output electrodes, compared to the other output electrodes and/or to the same output electrode at an earlier time, said one of the output electrodes corresponding to the intersection point.
In a further aspect of the invention there is provided a method of operating a touch sensitive display, said touch sensitive display comprising a sensor having an input array of electrodes and, capacitively coupled thereto, an output array of electrodes; said method comprising performing a scan operation at every intersection point of said input array, said scan operation comprising:    measuring a touch value for an intersection point;    determining the proportional difference between said touch value and a base touch value for said intersection point as a proportion of said base touch value, wherein said base touch value is indicative of there being no touch event on the sensor; and    comparing said proportional difference to a predetermined proportional touch threshold so as to determine whether there is a touch event at that point.
Various further aspects and features of the invention are defined in the claims.
Also described is a touch sensitive display comprising a sensor having an input array of electrodes and, capacitively coupled thereto, an output array of electrodes; wherein said touch sensitive display comprises a controller operable to:    perform a scan operation at every intersection point of said input array and output array, so as to obtain a touch value for every point, said touch value being indicative as to whether there is a touch event at that point, said intersection points being arranged into subsets;    compare said touch value to a predetermined first threshold; and    process only those subsets which comprise at least one intersection point that has a touch value exceeding the first threshold.
For the avoidance of doubt it should be appreciated that a touch value exceeding the threshold should not necessarily be taken to mean a touch value larger in magnitude. Where the touch value decreases from an untouched “base” value as a result of a touch, exceeding the first threshold will comprise the touch value falling below (in magnitude) the first threshold.
Said intersection points may be arranged in rows and columns, wherein said subsets are either said rows or said columns. In a specific embodiment, the controller is further operable to determine and compare the processing effort required in performing the processing step when said subsets are rows and in performing the processing step when said subsets are columns, and to select said subsets to be rows or columns according to which requires the least processing effort. Said determination may be based upon a determination of the number of rows having at least one intersection point that has a touch value exceeding the first threshold, a determination of the number of columns having at least one intersection point that has a touch value exceeding the first threshold, and the number of intersection points in each row and column.
Each of said subsets may have a counter attributed to it, said counter being incremented for each intersection point having a touch value exceeding the first threshold comprised within its corresponding subset. Alternatively, each of said subsets may have a binary flag attributed to it, said binary flag being set should its corresponding subset comprise an intersection point having a touch value exceeding the first threshold.
Said predetermined first threshold may be at a level lower than that of a touch threshold indicative of a touch event.
Also described is a touch sensitive display apparatus comprising:    a sensor comprising an input array of electrodes and, capacitively coupled thereto, an output array of electrodes;    a plurality of reception circuits, each reception circuit being operable to simultaneously receive a signal from a different electrode of said output array of electrodes;wherein said reception circuits each comprise an analogue to digital converter.
Each reception circuit may comprise a peak level detector and an amplifier.
Different subsets of said array of output electrodes may each be connected to a different reception circuit, such that each reception circuit is arranged to receive inputs from a particular subset of said array of output electrodes. Said output array of electrodes may be evenly distributed into said subsets. Said output array of electrodes may comprise parallel rows, said apparatus being arranged such that said output array of electrodes are distributed into said subsets in an interleaved manner, such that adjacent electrodes are not in the same subset and not connected to the same reception circuit. In one embodiment, where there are n reception circuits, each nth electrode of said array of output electrodes, in sequence, may be connected to the same reception circuit. “Row” in this context is not to be taken to imply a direction, and may mean vertical columns or rows arranged horizontally across the sensor.
Also described is a touch sensitive display comprising a sensor having an input array of electrodes and, capacitively coupled thereto, an output array of electrodes; wherein said touch sensitive display comprises a controller operable to: perform a scan operation at every intersection point of said input array and output array, so as to obtain a touch value for each intersection point, said touch value being indicative as to whether there is a touch event at the intersection point; and repeat said scan operation for only the intersection points for which the touch value meets a predetermined criteria, no further scan operations being performed for the intersection points for which the touch value does not meet said predetermined criteria.
Said controller may be operable to compare said touch value to a predetermined resample threshold, wherein said predetermined criteria comprises said touch value exceeding said predetermined resample threshold.
For the avoidance of doubt it should be appreciated that, a touch value exceeding the threshold here should not necessarily be taken to mean a touch value larger in magnitude. Where the touch value decreases from an untouched “base” value as a result of a touch, exceeding the predetermined resample threshold will comprise the touch value falling below (in magnitude) the predetermined resample threshold.
Said predetermined resample threshold may be at a level lower than of a touch threshold indicative of a touch event.
At each intersection point for which the scan operation is repeated, the results of the repeated scan operations may be averaged. Between 1 and 20 repeat scans may be performed for each of these intersection points.